1. Field of the Invention
The present invention relates to a process for the production of printed wiring boards with copper through-holes, i.e., copper through-hole printed wiring boards. According to the present process, the printed wiring boards can be produced in a shorter production time, and at a lower production cost, with a greatly increased reliability.
2. Description of the Related Art
In copper through-hole printed wiring boards, all circuits including through-holes are formed from copper, and thus have advantages such as a good adhesion of the solder resist thereto and a complete removal of the etching resist from the circuit area. These printed wiring boards are typically produced in accordance with the following three methods:
(1) hole-filling method; PA0 (2) tenting method; and PA0 (3) solder separation method. PA0 BI-1 2-n-propylbenzimidazole, PA0 BI-2 2-n-propylmethylbenzimidazole, PA0 BI-3 2-n-propyldimethylbenzimidazole, PA0 BI-4 2-n-butylbenzimidazole, PA0 BI-5 2-n-butylmethylbenzimidazole, PA0 BI-6 2-n-butyldimethylbenzimidazole, PA0 BI-7 2-n-pentylbenzimidazole, PA0 BI-8 2-n-pentylmethylbenzimidazole, PA0 BI-9 2-n-pentyldimethylbenzimidazole, PA0 BI-10 2-n-hexylbenzimidazole, PA0 BI-11 2-n-hexylmethylbenzimidazole PA0 BI-12 2-n-hexyldimethylbenzimidazole, PA0 BI-13 2-n-heptylbenzimidazole, PA0 BI-14 2-n-heptylmethylbenzimidazole, PA0 BI-15 2-n-heptyldimethylbenzimidazole, PA0 BI-16 2-n-octylbenzimidazole, PA0 BI-17 2-n-octylmethylbenzimidazole PA0 BI-18 2-n-octyldimethylbenzimidazole, PA0 BI-19 2-n-nonylbenzimidazole, PA0 BI-20 2-n-nonylmethylbenzimidazole, PA0 BI-21 2-n-nonyldimethylbenzimidazole, PA0 BI-22 2-n-decylbenzimidazole, PA0 BI-23 2-n-decylmethylbenzimidazole PA0 BI-24 2-n-decyldimethylbenzimidazole, PA0 BI-25 2-n-undecylbenzimidazole, PA0 BI-26 2-n-undecylmethylbenzimidazole, PA0 BI-27 2-n-undecyldimethylbenzimidazole, PA0 BI-28 2-n-dodecylbenzimidazole, PA0 BI-29 2-n-dodecylmethylbenzimidazole PA0 BI-30 2-n-dodecyldimethylbenzimidazole, PA0 BI-31 2-n-tridecylbenzimidazole, PA0 BI-32 2-n-tridecylmethylbenzimidazole, PA0 BI-33 2-n-tridecyldimethylbenzimidazole, PA0 BI-34 2-n-tetradecylbenzimidazole, PA0 BI-35 2-n-tetradecylmethylbenzimidazole, PA0 BI-36 2-n-tetradecyldimethylbenzimidazole, PA0 BI-37 2-n-pentadecylbenzimidazole, PA0 BI-38 2-n-pentadecylmethylbenzimidazole PA0 BI-39 2-n-pentadecyldimethylbenzimidazole, PA0 BI-40 2-n-hexadecylbenzimidazole, PA0 BI-41 2-n-hexadecylmethylbenzimidazole, PA0 BI-42 2-n-hexadecyldimethylbenzimidazole, PA0 BI-43 2-n-heptadecylbenzimidazole, PA0 BI-44 2-n-heptadecylmethylbenzimidazole, PA0 BI-45 2-n-heptadecyldimethylbenzimidazole, PA0 BI-46 2-isopropylbenzimidazole, PA0 BI-47 2-isopropylmethylbenzimidazole, PA0 BI-48 2-isopropyldimethylbenzimidazole, PA0 BI-49 2-isobutylbenzimidazole, PA0 BI-50 2-isobutylmethylbenzimidazole PA0 BI-51 2-isobutyldimethylbenzimidazole, PA0 BI-52 2-isopentylbenzimidazole, PA0 BI-53 2-isopentylmethylbenzimidazole, PA0 BI-54 2-isopentyldimethylbenzimidazole, PA0 BI-55 2-isohexylbenzimidazole, PA0 BI-56 2-isohexylmethylbenzimidazole, PA0 BI-57 2-isohexyldimethylbenzimidazole, PA0 BI-58 2-neopentylbenzimidazole, PA0 BI-59 2-neopentylmethylbenzimidazole, PA0 BI-60 2-neopentyldimethylbenzimidazole, PA0 BI-61 2-sec.-butylbenzimidazole, PA0 BI-62 2-sec.-butylmethylbenzimidazole PA0 BI-63 2-sec.-butyldimethylbenzimidazole, PA0 BI-64 2-tert.-butylbenzimidazole, PA0 BI-65 2-tert.-butylmethylbenzimidazole, PA0 BI-66 2-tert.-butyldimethylbenzimidazole, PA0 BI-67 2-phenylbenzimidazole, PA0 BI-68 2-phenylmethylbenzimidazole, PA0 BI-69 2-phenyldimethylbenzimidazole, PA0 BI-70 2-tosylbenzimidazole, PA0 BI-71 2-tosylmethylbenzimidazole, PA0 BI-72 2-tosyldimethylbenzimidazole, PA0 BI-73 2-xylylbenzimidazole, PA0 BI-74 2-xylylmethylbenzimidazole PA0 BI-75 2-xylyldimethylbenzimidazole, PA0 BI-76 2-mesitylbenzimidazole, PA0 BI-77 2-mesitylmethylbenzimidazole, PA0 BI-78 2-mesityldimethylbenzimidazole, PA0 BI-79 2-tert.-phenylbenzimidazole, PA0 BI-80 2-tert.-phenylmethylbenzimidazole, PA0 BI-81 2-tert.-phenyldimethylbenzimidazole, PA0 BI-82 2-(1-phenylmethyl)benzimidazole, PA0 BI-83 2-(3-phenylpropyl)benzimidazole, PA0 BI-84 2-(7-phenylheptyl)benzimidazole, PA0 BI-85 2-(2-phenylethyl)methylimidazole, PA0 BI-86 2-(2-tolylethyl)benzimidazole, and PA0 BI-87 2-(2-tolylethyl)methylimidazole.
The hole-filling method comprises drilling a necessary numbers of holes in a predetermined portion of the double-sided copper clad laminate, and subjecting the holes-bearing laminate to a sequential chemical copper plating and copper electroplating. After the electroplating is completed, all of the holes are filled with a sealing ink, to protect an inner wall of the each through-hole from the introduction of an etchant in the subsequent etching step. Thereafter, positive resist patterns corresponding to the necessary circuit patterns are applied to both sides of the laminate, by a printing process or photographic process, and then an etching is carried out, using the resist patterns as a mask, to remove the copper exposed by the resist pattern. Finally, the resist patterns and the sealing ink in the holes are removed, to obtain the intended copper through-hole printed wiring boards.
The tenting method is characterized by using a dry resist film in place of the sealing ink of the above hole-filling method. Namely, after the completion of drilling, chemical copper plating and copper electroplating, dry resist films are applied to both sides of the laminate, and the holes are covered with these films. The resist films are patternwise exposed and developed, followed by etching using the remaining resist films as a mask, to remove the exposed copper. Note, an inner wall (copper plating) of the through-holes is protected by the upper and lower resist films. The copper through-hole printed wiring boards are obtained after removal of the remaining resist films.
The solder separation method is distinguished from the above-described methods in that it utilizes negative patterns of a plating resist for a solder electroplating (the resist is not etched). A sealing ink is not required in this method. After the drilling, chemical copper plating and copper electroplating are completed as in the above two methods, negative patterns of the plating resist are applied to the copper clad laminate by a printing or photographic process. Then, using the negative resist patterns as a mask, a solder electroplating is carried out to deposit the solder on the exposed copper surfaces. Thereafter, the resist patterns used as the mask and the exposed copper plating not having a deposit of solder thereon are removed, to obtain the copper through-hole printed wiring boards.
The above-discussed prior art methods, however, have several drawbacks. For example, because of a poor reliability of the etching resist layer used, defective products are frequently produced, and although the production efficiency is accordingly not high, the production cost is remarkably high. Particularly, these methods can not satisfy recent requirements that a large amount of products must be provided with a shorter delivery time and at a lower cost. Further, in the solder separation method, due to the use of hydrofluoric acid and lead used in the processing steps thereof, a problem of environmental pollution can not be avoided, and accordingly, the expense of preventing environmental pollution is remarkably increased.